Nicotine is the main addictive component of tobacco, and its behavioral and pharmacological effects are initiated by binding to neuronal nicotine acetylcholine receptors (nAChRs). Nicotine delivered by cigarette increasing the heart rate and blood pressure. The onset and duration of nicotine's peripheral effects vary. For instance, during habitual smoking, nicotine tolerance to the blood pressure effects develops faster than to the heart rate effects. Evidence suggests that the changing levels of nAChR desensitization are mechanistically linked to the development of tolerance, and desensitization and pharmacology are in turn linked to the subunit composition of the nAChRs. Although there are many in vitro studies that associated the functional properties of the receptors to their subunit composition, there are no in vivo studies that examine the systems level relationships between particular nAChR subunits and nicotine's effects. The guiding hypothesis of this proposal is that the subunit composition of nAChRs dictates the complex cardiovascular effects of nicotine, including the development of tolerance. To test our hypothesis, we will use in vivo and in vitro techniques to study mutant mice lacking nAChR subunits that are known to be expressed in the homeostasis, we will monitor blood pressure and the heart rate via radio-telemetry under basal conditions and in response to nicotine administrations. Radio-telemetry measures physiological signals and transmits them to distant receivers, thereby minimizing experimental artifacts arising from stress. The in vivo experiments will be accompanied by in vitro studies on cardiac contractility in response to nicotine and to adrenergic and cholinergic agonists. Receptor binding and in situ hybridization experiments will be conducted in collaboration with the Morphology Core to determine possible compensatory mechanisms as well as nAChR subunit up- regulation after chronic exposure to nicotine. Patch-clamp experiments in collaboration with Dr. Dani will provide information on the biophysical profile of nAChR currents in autonomic ganglia.